Two-way relay underwater acoustic communications with multiuser decision-feedback detection and relay preprocessing

A two-way relay underwater acoustic communication (TWR-UAC) scheme is proposed and investigated, where communication between a pair of terminals is assumed. In our studies, underwater acoustic (UA) channels are modeled as the sparse multipath channels experiencing Rayleigh fading. A novel relaying protocol is proposed to exploit the long transmission delay of sound in water. It can be shown that this protocol is capable of increasing the throughput of UAC systems, when half-duplex mode is assumed. At the relay, minimum mean-square error decision feedback detection (MMSE-DFD) and MMSE-assisted preprocessing are invoked, in order to mitigate multiuser interference (MUI) and inter-symbol interference (ISI), as well as to reduce the complexity of communication terminals. Our studies and performance results show that the proposed TWR-UAC system is capable of achieving promising error performance, by making use of both the multipath diversity and the spatial diversity provided by the transducer array of the relay.